My mom is moving from Maryland to Pennsylvania and is bedridden. Can I change her address on her ID at the DMV with a power of attorney?

No would be my answer. Government entities do not usuallyrecognize POA. I had to take my Mom, who needed a walker, to the DMV. She hadto sign her paperwork in front of them. With Dementia she could not even spell her name correctly. Then she had to stand for a picture.

If bedridden, what is Mom going to need an ID for? If hers is not expired, continue to use it till it does. If asked why the address is different, tell them thats her main residence.

Milz2025: Pose your question to the DMV.

This would be best answered by the DMV of the State she is moving to.
If she is going to be in a Facility some have arrangements with the DMV and they will send employees to Facilities to get residents the ID's or licenses they need.
If mom is going to be living with you I would get her settled first and get all the other change of address done. (insurance, Social Security and any other important changes.) Once that is done and she is getting mail at your house you can use that to present to the DMV. If they truly need her to appear call for a Medical Transport and make an appointment at the DMV.

Why not call them and ask?
That's your best chance of the RIGHT answer.
Remember, we aren't experts, and we come from all over the country and sometimes from other states.
Good luck.